A conventional image match-point detection technique performs an operation such as SAD (Sum Absolute Difference) to many pixel values to detect the match between images by searching for the points of small image difference (refer to Japanese Patent Laid-Open Publication No. 2008-39491).
The SAD, however, requires direct comparison among a plurality of pixel values. Direct comparison is necessary among many pixel values even in searching for one match point. This results in an enormous amount of operation.
For the reason above, a technique has been devised that downscales images to lower the resolution, thereby decreasing the amount of data to be compared, and gradually raises the resolution in searching for the match (refer to Japanese Patent Laid-Open Publication No. 1998-136304). Nevertheless, this technique also requires comparison among pixel values, and hence has a difficulty in drastic reduction of operation amount. In addition, this technique has problems such as detection error in periodic patterns and noises. Therefore, this technique has conventionally low accuracy of match-point detection. Moreover, this technique requires further comparison circuits with an increased amount of operation when rotation of images due to inclination of a camera, movement of a camera in the forward and backward directions, zoom scaling, etc. are taken under consideration.
Japanese Patent Laid-Open Publication No. 2005-295495 discloses a technique of correcting blurred images due to camera shake by extracting a specific number of characteristic points.
Camera movement and shake can be more accurately identified, as match points (characteristic points) are detected more. As match points are detected more, however, the amount of operation increases. Therefore, it causes a higher cost and a larger size, resulting in limited use. Or, the tracking range of movement of a camera or an object to be photographed is conventionally limited.
Moreover, noise reduction, brightness of an object to be photographed, etc. have to be considered before a match-point detection process. Otherwise, the process cannot be put in practical use. The process, therefore, requires improvements such as use of RRF (Radical Reach Filter) which results in further increased amount of operation.